1. Field of the Invention
The present invention relates to a fabrication method of a circuit substrate. More particularly, the present invention relates to a fabrication method of a rigid-flex circuit board.
2. Description of Related Art
A rigid-flex circuit board is a printed circuit board comprised of a flexible circuit board and a rigid circuit board, and therefore the rigid-flex circuit board is characterized by flexibility of the flexible circuit board and rigidity of the rigid circuit board. When the rigid-flex circuit board is fabricated, the flexible circuit board containing intrinsic circuits serves as a core layer, and circuits in the rigid circuit board are formed on the flexible circuit board by performing a build-up process or a lamination process. A flexible portion of the flexible circuit board is exposed by a gap of the rigid circuit board, and a routing process is then performed by a cutting machine, so as to form the required number of rigid-flex circuit boards with a designated shape.
FIG. 1 is a schematic cross-sectional view of a conventional rigid-flex circuit board. In FIG. 1, a substrate 110 is bonded to a flexible circuit board 130 through a cover layer 120 for forming a rigid-flex circuit board 100. The substrate 110 has a prepreg 112 and a patterned conductive layer 114 disposed on the prepreg 112. The flexible circuit board 130 has a flexible portion F exposed by an opening OP1 of the prepreg 112, such that the rigid-flex circuit board 100 equipped with the flexible portion F is characterized by flexibility.
According to the pertinent art, when the prepreg 112 is laminated to the flexible circuit board 130, the prepreg 112 is prone to be distorted, such that a portion of squeeze 116 overflows into the opening OP1 and partially covers the flexible portion F of the flexible circuit board 130. However, as the flexible portion F is partially covered by the squeeze 116, the flexibility of the rigid-flex circuit board 100 is significantly reduced. In addition, the squeeze 116 covering the flexible portion F is not apt to be removed, and it is thus likely for the squeeze to remain, which may pose an impact on yield in subsequent manufacturing processes.